When George Zimmerman and his girlfriend called 911 in the heat of a domestic dispute, they almost certainly knew that they were not just talking to the emergency dispatcher. In the age of Twitter and the 24-hour news cycle, experts say a call to central dispatch can quickly become public, and is often manipulated to spin a story or even lay the groundwork for a criminal defense.

"There really has been what I would call a multiyear training program in place, frankly" to use 911 calls strategically, says former Massachusetts prosecutor Wendy Murphy. "And folks, especially people who understand high-profile crimes and the nature of evidence and the rules of evidence and domestic abuse generally, they (know) the power of a 911 call to change not only the trajectory of the case, but to change public opinion and to affect the jury pool."

On Monday, 27-year-old Samantha Scheibe called Seminole County, Fla., dispatchers and accused Zimmerman, the former neighborhood watchman, of pointing a shotgun at her, smashing a coffee table and pushing her. Around the same time, the Sanford man made a 911 call of his own, stating that he did not threaten Scheibe, and that it was she who had broken the table.

"Didn't Zimmerman sound way too calm?" says the Miami lawyer, who represented former Panamanian dictator Manuel Noriega. "He knows well — and everybody else knows — that those tapes are admissible in court, and it's a way for him to make a positive statement on a very bad situation."

This is the third time since Zimmerman's fatal shooting of an unarmed black teenager in February 2012 that 911 calls have played a major role in the Florida man's future. Not long after his July acquittal in the killing of 17-year-old Trayvon Martin, Shellie Zimmerman initially told a dispatcher that her estranged husband had smashed the iPad on which she was recording him, and was threatening her and her father with a gun.

In 2006, the U.S. Supreme Court determined that the use of some 911 calls as evidence did not violate a defendant's Sixth Amendment right to confront and cross-examine his accuser. These "excited utterance" exceptions to the rules involving hearsay are especially crucial in domestic violence cases, in which the victim might be reluctant or even unable to testify, says Murphy.

As a result, she says, victims began to think "strategically" about using 911 calls as a way to have their accusations entered into the record without necessarily having to testify, says Murphy, now an adjunct professor at New England Law in Boston.

Rubino says it behooved Zimmerman to come across as un-excited as possible.

"It's like he was trying to be really calm and saying, 'My crazy girlfriend is doing all this stuff,'" Rubino says. "I think he was trying to create a defense."

In the September incident, Shellie Zimmerman later acknowledged she did not see a gun, and no charges were filed. This time, Zimmerman, 30, faces a felony charge of aggravated assault, as well as misdemeanor counts of battery and criminal mischief.

Murphy says the unwritten rule in such cases has been "whoever calls first wins." But because the police know that people can be crafty, she says, "they don't weigh that factor as much as they used to in determining which of two people is the real victim."

From his experience in the Trayvon Martin case, it's clear that Zimmerman knew his 911 call would be both a powerful evidentiary and public relations tool, says Ken LaMance of San Francisco, general counsel for LegalMatch.com.

"So it's almost as if he's making statement about the case beforehand — especially if he's not planning on testifying in the future" says LaMance. "It allows him to speak without the fear of cross-examination. So if he can get his side out, and in a clear way, he never has to face the other side asking him questions or follow-ups."

But LaMance says it's also safe to assume that Scheibe knew any allegations she made against her infamous boyfriend would immediately go viral — as would her 911 recording.